Wind power has been harnessed by windmills for hundreds of years and commonly this has been accomplished by large windmill blades slowly turning a shaft from the force of the wind to pump water or rotate machinery. Modern attempts to utilize the force of wind to generate electrical power has suffered from the problems of widely varying wind velocity. Unfortunately, it is not normally possible to control wind velocity which is known to vary from zero to one hundred and more miles per hour.
A wind driven propeller designed to operate efficiently at some intermediate wind velocity such as 20-30 miles per hour will be rotated at such a high speed by winds of say 100 m.p.h. as to be self destructive. Additionally, such a propeller will operate at a very low efficiency at low wind velocities, such as 10 m.p.h. so as to be impracticable for power generation at low wind velocities. The foregoing limitations pose very real practical difficulties inasmuch as most windy geographical locations do experience quite large variations in wind velocities.
It is also known that a tower or the like upon which a wind driven propeller is mounted creates a "shadow effect" by changing the wind pattern on each blade as it aligns with the tower during propeller rotation. This creates an unbalance which is of small importance with slow moving propellers, however, with high speed propellers this unbalance causes vibrations that are damaging to bearings, the tower, and the like, mounting the propeller.